Air Handler Fan Speed - Home Energy Pros2015-03-31T21:18:26Zhttp://homeenergypros.lbl.gov/forum/topics/air-handler-fan-speed?commentId=6069565%3AComment%3A122745&xg_source=activity&feed=yes&xn_auth=nothis is what I do for 25 yr.…tag:homeenergypros.lbl.gov,2013-07-08:6069565:Comment:1237362013-07-08T13:07:41.394ZEric Kjelshushttp://homeenergypros.lbl.gov/profile/EricKjelshus
<p>this is what I do for 25 yr. I find most res unit are mid .8" water Col. The tag on side of air mover says .5 or .4</p>
<p>you can look at SP or feet per min or temp, you get the same model. This is big, very big</p>
<p>this is what I do for 25 yr. I find most res unit are mid .8" water Col. The tag on side of air mover says .5 or .4</p>
<p>you can look at SP or feet per min or temp, you get the same model. This is big, very big</p> A quick static pressure test…tag:homeenergypros.lbl.gov,2013-07-08:6069565:Comment:1237322013-07-08T11:49:47.826ZJustin Mackovyakhttp://homeenergypros.lbl.gov/profile/JustinMackovyak71
<p>A quick static pressure test would help you determine if you're getting the flow you need over the coil. You should be able to reference your manufacturer's documentation for the TESP. If it's too high, then it would be time to call in for a clean and tune as well as test and balance. </p>
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<p>Just my $0.02.</p>
<p>A quick static pressure test would help you determine if you're getting the flow you need over the coil. You should be able to reference your manufacturer's documentation for the TESP. If it's too high, then it would be time to call in for a clean and tune as well as test and balance. </p>
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<p>Just my $0.02.</p> Sounds like to me that you ha…tag:homeenergypros.lbl.gov,2013-07-05:6069565:Comment:1233352013-07-05T04:20:21.987ZTarheelTechhttp://homeenergypros.lbl.gov/profile/TarheelTech
<p>Sounds like to me that you have a system installed and it has never been setup properly. Have a Service Tech come by and set it up for you.</p>
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<p>Sounds like to me that you have a system installed and it has never been setup properly. Have a Service Tech come by and set it up for you.</p>
<p></p> Sounds like the unit may not…tag:homeenergypros.lbl.gov,2013-06-29:6069565:Comment:1226972013-06-29T21:34:48.129ZBob Blanchettehttp://homeenergypros.lbl.gov/profile/BobBlanchette
<p>Sounds like the unit may not be charged correctly if it's not full?</p>
<p>Sounds like the unit may not be charged correctly if it's not full?</p> Use your IR with new 16 seer…tag:homeenergypros.lbl.gov,2013-06-29:6069565:Comment:1226872013-06-29T13:59:18.070ZEric Kjelshushttp://homeenergypros.lbl.gov/profile/EricKjelshus
Use your IR with new 16 seer coils and see hot spot. All the coil is not full.
Use your IR with new 16 seer coils and see hot spot. All the coil is not full. I'm always amused by HVAC con…tag:homeenergypros.lbl.gov,2013-06-29:6069565:Comment:1228132013-06-29T12:56:08.298ZCurt Kinderhttp://homeenergypros.lbl.gov/profile/CurtKinder
<p>I'm always amused by HVAC contractors who blame 410a for whatever woes are at hand.</p>
<p>The cost delta for an ECM blower equipped air handler is now about $300, and for another $200 deploy a thermostat that senses and signals the air handler that humidity is high. Most decent AHUs now have a dehu feature that drops airflow by 15% or so in response to the dehu signal.</p>
<p>Don't overdo the reduced airflow thing - cabinet and nearby ductwork may sweat and ultimately evaporator will ice,…</p>
<p>I'm always amused by HVAC contractors who blame 410a for whatever woes are at hand.</p>
<p>The cost delta for an ECM blower equipped air handler is now about $300, and for another $200 deploy a thermostat that senses and signals the air handler that humidity is high. Most decent AHUs now have a dehu feature that drops airflow by 15% or so in response to the dehu signal.</p>
<p>Don't overdo the reduced airflow thing - cabinet and nearby ductwork may sweat and ultimately evaporator will ice, wreaking all manner of mayhem.</p>
<p>Excessive RH is nearly always a building science issue (excess building or ductwork air leakage, poor point source ventilation) rather than an HVAC issue unless the system is oversized</p>
<p>Despite a swampy outdoor dewpoint of 70+, my home is at 77*F / 45% RH. That's with no central dehu.</p>
<p>It is my contention that separate central dehus are an expensive (both to buy and to run) band-aid masking some other screwup. I yanked two out of a home recently while in the course of right-sizing the HVAC and fixing air leakage.</p> When used with a TXV (most 41…tag:homeenergypros.lbl.gov,2013-06-29:6069565:Comment:1227452013-06-29T12:14:40.006ZBob Blanchettehttp://homeenergypros.lbl.gov/profile/BobBlanchette
<p>When used with a TXV (most 410a systems use them) you can get the coil as cold as you want simply by reducing airflow. No need to use a smaller coil</p>
<p>When used with a TXV (most 410a systems use them) you can get the coil as cold as you want simply by reducing airflow. No need to use a smaller coil</p> I have tryed that but with th…tag:homeenergypros.lbl.gov,2013-06-29:6069565:Comment:1228042013-06-29T03:42:00.621ZEric Kjelshushttp://homeenergypros.lbl.gov/profile/EricKjelshus
<p>I have tryed that but with the new R-410A I now get higher temps than ever. To get very high RH humid removal I all so put smaller coils in so the coil gets very coil, but the EER goes low at same time. I have been adding a dehumidfier sized to building and get lower energy use over all. Like a Honey well or desert air then we get around 50% leaval if the building is sealed </p>
<p>I have tryed that but with the new R-410A I now get higher temps than ever. To get very high RH humid removal I all so put smaller coils in so the coil gets very coil, but the EER goes low at same time. I have been adding a dehumidfier sized to building and get lower energy use over all. Like a Honey well or desert air then we get around 50% leaval if the building is sealed </p> Ideally you would set the blo…tag:homeenergypros.lbl.gov,2013-06-29:6069565:Comment:1227332013-06-29T01:33:23.478ZBob Blanchettehttp://homeenergypros.lbl.gov/profile/BobBlanchette
<p>Ideally you would set the blower up as a "2 speed" with a humidity controlled blower speed. Run 350CFM/ton during humid weather and 450CFM/ton during dry weather. Get the coil down to 35-40 degrees in humid weather for maximum humidity removal, and 45-50 degrees for maximum EER during dry weather. A simple 2 stage thermostat can be wired to do this, run low speed most of the time and boost blower speed when cooling demand is high. System must be sized correctly for this strategy to work. If…</p>
<p>Ideally you would set the blower up as a "2 speed" with a humidity controlled blower speed. Run 350CFM/ton during humid weather and 450CFM/ton during dry weather. Get the coil down to 35-40 degrees in humid weather for maximum humidity removal, and 45-50 degrees for maximum EER during dry weather. A simple 2 stage thermostat can be wired to do this, run low speed most of the time and boost blower speed when cooling demand is high. System must be sized correctly for this strategy to work. If the system is oversized high blower will never activate.</p>
<p>For heat I recommend running delta T near the bottom of the range. Keeping a high volume of air moving helps with stratification issues, especially if vents are located in ceiling. It also allows more wiggle room as the filter gets dirty over time.</p> You are correct in stating th…tag:homeenergypros.lbl.gov,2013-06-27:6069565:Comment:1226142013-06-27T13:48:29.840ZDoug Garretthttp://homeenergypros.lbl.gov/profile/DougGarrett
<p>You are correct in stating that the blower fan is set to different speeds for heating and cooling. For cooling the evaporator coil is designed to operate at peak efficiency with between 350 and 450 CFM per ton of cooing capacity. Most equipment comes with the fan speed set in cooling mode at 400 CFM/ton. </p>
<p>The greater the airflow over the coil, the less humidity you remove, so if you live in a dry climate, you can set the fan speed up to as much as 450/ton to get more sensible…</p>
<p>You are correct in stating that the blower fan is set to different speeds for heating and cooling. For cooling the evaporator coil is designed to operate at peak efficiency with between 350 and 450 CFM per ton of cooing capacity. Most equipment comes with the fan speed set in cooling mode at 400 CFM/ton. </p>
<p>The greater the airflow over the coil, the less humidity you remove, so if you live in a dry climate, you can set the fan speed up to as much as 450/ton to get more sensible cooling and less latent. If you live in a humid summer climate, you may benefit from slowing the fan down to as little as 350/ton to improve humidity control in your home. Do not go much below 350/ton or you can cause the coil to ice because you aren't moving enough warm air over it to keep it from freezing! For example, a dirty or highly restrictive air filter can reduce airflow to the point that a coil will ice up. </p>
<p>On the heating side the needed airflow is also related to the BTU's being produced but this time we are looking at the firebox. We need sufficient airflow to remove the heat being produced to keep the firebox below the safety cutoff temperature which is usually 130-135F. If you set the fan speed too low, the firebox will get too hot because there is not enough airflow to carry the heat away and your unit will shut down on a high heat overload safety cutoff. This is why a dirty filter can sometimes cause your furnace to short cycle and shutoff before reaching the thermostat set point. If you set the airflow too high the air coming out of your registers will be too cool and your system efficiency and your comfort will suffer. </p>
<p>We usually set the fan speed to keep the temperature rise of the air passing through the system between roughly 40F-65F depending on the age and efficiency of your system. So, return air temperature may be 70F which means that the supply air measured in the furnace would be 110F to 135F. The correct range for the temperature rise is usually stated on the nameplate of the furnace. Most 90+ furnaces are rated at around 50F temperature rise for example. By the way, the HVAC folks call this difference between input and exiting air temperatures, the Delta T of the cooling or heating mode. </p>
<p>This is the formula that determines the relationship between Delta T and airflow to BTU's produced:</p>
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<p>[(Delta T) x 1.08] x CFM = BTU output</p>
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<p>I hope this helps.</p>
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